This invention relates to powder coating compositions. More particularly, the invention relates to powder coating compositions comprising at least one thermosetting resin and at least one poly(phenylene ether).
Organic solvent type coatings, which are obtained by dissolving main components such as resin and the like in an organic solvent and adding thereto auxiliary components such as coloring agent, curing agent and the like, have heretofore been used widely in coating applications. However, the problems of these organic solvent type coatings, such as fire hazard, adverse effect on safety and hygiene, environmental pollution and the like, has resulted in increased attention being paid to coatings which vaporize no organic solvent, particularly aqueous emulsion type coatings and powder coatings.
Aqueous emulsion type coatings, however, also have drawbacks. For example in producing such a coating resin particles and a pigment are typically dispersed stably in an aqueous medium and therefore a hydrophilic substance such as emulsifier or the like is used, the film formed with the coating is inevitably inferior in properties such as water resistance, alkali resistance and the like; moreover, the film often has low adhesivity to a material to be coated; further, it takes a time to obtain a dried film, as compared with the case of an organic solvent type coating and, in order to complete film drying in a short time, special equipment and a high cost are required.
In contrast, powder coatings, which contain no organic solvent, have various excellent advantages. For example, they have very low volatile organic content and give off very little volatile material to the environment when cured; they are free from fire hazard, adverse effect on safety and hygiene, environmental pollution, or the like; they can be stored in an ordinary storehouse; the amount of ventilation air in a spray booth can be a minimum and the ventilation air can be recirculated, resulting in high energy efficiency; and the coating film obtained has no foams which are generated by the vaporization of solvent during film drying. Powder coatings have further advantages. For example, they can be used as they are without the necessity of adjusting the viscosity, solid content, etc.; and they can be easily recovered without staining the operation site and producing any waste. Furthermore, powder coatings can be applied by automated coating procedures and, in view of the total cost including cost of materials, pretreatment cost, cost of coating operation, equipment cost, etc., are very economical as compared with organic solvent type coatings and aqueous emulsion type coatings.
Powder coatings generally comprise a solid film-forming resin, often with one or more pigments. They can be thermoplastic-based but are more usually thermoset-based, typically incorporating two co-reactive film-forming resins or incorporating a curing agent for a film-forming resin in the powder particles.
Heretofore, powder coatings which contain primarily an epoxy resin and a curing agent have been employed in the art, and although these generally have good chemical resistance, adhesion, and surface hardness, etc., they often exhibit less than optimal mechanical properties such as inadequate fracture toughness. Therefore, the present inventors, as a result of an intensive investigation aiming at development of a powder coating composition have found a thermoset composition for powder coatings which can provide a coating layer with improved fracture toughness and other properties without loss of chemical resistance, adhesion, and surface hardness, etc. which are characteristics in typical epoxy resin-based powder coatings.
One aspect of the invention is a powder coating composition comprising at least one thermosetting resin and at least one poly(phenylene ether).
Another aspect of the invention is a process for making a powder coating composition which comprises combining at least one thermosetting resin and at least one poly(phenylene ether).
Still another aspect of the invention is an article coated with a powder coating composition comprising at least one thermosetting resin and at least one poly(phenylene ether). Yet another aspect of the invention is an article coated with a cured powder coating composition comprising at least one thermosetting resin and at least one poly (phenylene ether).